1. Field of the Invention
The invention relates to a sheet feeding apparatus for sending warm air to a sheet to be fed.
2. Related Background Art
There has been proposed a construction for flowing warm air against paper in a sheet feeding paper deck mounted on an image forming apparatus such as a copying machine to thereby loosen the paper (for example, Japanese Patent Application Laid-Open No. 2001-048366).
In this example of the prior art, basically the temperature controlling operation of an air heater and a sheet loosening operation (for example, the start of fan rotation and the start of swing shutter motor rotation) are started at a time. That is, the fan starts rotation simultaneously with the start of the temperature control of the air heater.
Therefore, much time is required until the air heater temperature, i.e., warm air temperature assumes a predetermined value, and this leads to the disadvantage that the time until the loosening operation is terminated and the sheet feeding operation becomes possible is slow with a result that the performance of the entire apparatus is lowered.
Also, in order to avoid the above-noted disadvantage peculiar to the above-described example of the prior art, there is conceivable a construction for starting the loosening operation before the air heater temperature reaches the predetermined value, but in this case, the loosening operation (air assisting operation) is started before the warm air temperature rises sufficiently, and this leads to the disadvantage that loosening becomes insufficient.
Generally, in an air assisting construction wherein warm air is blown against the sheets in the paper deck to thereby loosen the sheets to reliably loosen the sheets, it is necessary to flow warm air of a predetermined temperature or higher for a predetermined value of time or longer, and flowing air of a temperature lower than the predetermined temperature is little effective for the loosening of the paper. Also, in case of blowing an air of low temperature against the sheets of paper, the sheets of paper may get damp. As a result, this may affect the loosening operation, and deteriorate quality of images to be formed on the sheets of paper.